The present invention relates generally to a Instantaneous Frequency Measurement (IFM) receiver with means to resolve an ambiguity in multiple frequency estimation, and more particularly to means to resolve the 2.pi. ambiguity in multiple frequency estimation of complex signals.
The following United States patents are of interest.
U.S. Pat. No. 4,904,930--Nicholas PA1 U.S. Pat. No. 4,937,583--Poinsard PA1 U.S. Pat. No. 4,963,816--Tsui et al PA1 U.S. Pat. No. 5,036,324--Lamper et al PA1 U.S. Pat. No. 5,099,194--Sanderson et al PA1 U.S. Pat. No. 5,099,243--Tsui et al PA1 U.S. Pat. No. 5,109,188--Sanderson et al PA1 U.S. Pat. No. 5,117,238--Silverstein et al PA1 U.S. Pat. No. 5,122,732--Engeler et al PA1 (1) The method can resolve M frequencies with (M+1) FFT units operating in parallel. PA1 (2) The method provides a noise protection of q(Hz) which can be increased at the expense of bandwidth. PA1 (3) For reasonable levels of noise protection, the system bandwidth can be expanded by an order of magnitude as compared with the bandwidths of the FFT units. Much greater bandwidths can be realized if a three FFT unit single frequency resolution algorithm is employed. PA1 (4) The use of a two FFT unit, single frequency 2.pi. ambiguity resolution algorithm can be implemented with commercially available ROMs. PA1 (5) The entire invention lends itself to parallel processing.
A paper of interest is:
W. McCormick, J. B. Y. Tsui, V. L. Bakke, "A Noise Insensitive Solution to an Ambiguity Problem in Spectra Estimation," IEEE Transactions on Aerospace and Electronic Systems. Vol. 25, No. 5, Sep. 1989, pages 729-732.
The paper discloses a design procedure using the Chinese Remainder Theorem for solving a congruence problem of number theory for a given amount of noise protection, a stated frequency resolution, a minimum bandwidth and a fixed level of precision (bits) in a IFM receiver.
The references cited in the paper are also of interest. The invention is conceptually similar to the range ambiguity resolution problem in multiple prf pulse/doppler radar. See Skolnik, M. J. (Ed.) Radar Handbook, New York: McGraw Hill, 1970, pages 19-12 to 19-16.
Tsui et al in U.S. Pat. No. 4,963,816 disclose an Instantaneous frequency measurement receiver having two delay lines wherein frequency resolution is based on the Chinese Remainder Theorem. The theorem states that if an unknown number X is divided by a number a with a remainder r.sub.1 and also divided by a number b with a remainder r.sub.2, where a and b are relatively prime numbers, the number X can be determined uniquely from a, b, r.sub.1 and r.sub.2 if X&lt;ab. For example, if a=5, b=7, r.sub.1 =2 and r.sub.2 =1, the Chinese remainder gives an X of 22.
Lamper et al in U.S. Pat. No. 5,036,324 disclose a pulse compression technique for a high duty rate radar, wherein a processor 16 employs parallel processing architecture utilizing Fast Fourier Transforms (FFT). FFT section of vector processor 106 includes three identical FFT units or engines 112a, 112b and 112c, respectively, which operate independently of each other and are separately programmable by the CPU.
Sanderson et al in U.S. Pat. No. 5,099,194 disclose a digital frequency measurement receiver with bandwidth improvement through multiple sampling of real signals. Two sets of uniform samples are used with slightly different sampling frequency, wherein each set is Fourier transformed independently and the frequency of the lowest aliases determined. Unambiguous determination of the signal frequency over a range far exceeding the Nyquist frequency is obtained except at a discrete set of points.
Tsui et al in U.S. Pat. No. 5,099,243 disclose a technique for extending the frequency range of a digital frequency measurement receiver, through multiple sampling of complex signals, which employs in-phase and quadrature components of the signal coupled with non-uniform sampling. Each set of complex samples is independently Fourier transformed, and the frequency of the lowest aliases permits unambiguous determination of the signal frequency over a range far exceeding the Nyquist frequency.
Sanderson et al in U.S. Pat. No. 5,109,188 disclose a technique for extending the frequency range of an instantaneous frequency measurement receiver, wherein a power divider is employed with two outputs. One output is supplied to a first A/D converter, and the other output is supplied via a delay device to a second A/D converter. A processor 60 receives the outputs of the two A/D converters 42, 44. The input signal is subjected to a known delay .tau. and both original and delayed signals are sampled simultaneously and Fourier transformed and both the phase and amplitudes calculated.
Silverstein et al in U.S. Pat. No. 5,117,238 and Enoeler et al in U.S. Pat. No. 5,122,732 utilize a matrix based super resolution spectral estimation algorithms and parallel architectures. An embodiment utilizes a windowing element and FFT to perform low pass filtering. Various embodiment are disclosed.
The remaining patent references are included for general background information.